1. Field of the Invention
The present invention relates to a serial recording method and apparatus applicable to an office equipment or communication equipment such as a facsimile terminal equipment, a copying machine, a word processor, an electronic typewriter, a personal computer, or an office computer, and in particular preferably useful for the facsimile terminal equipment.
A preferred embodiment of the present invention is one of using an ink jet recording method of recording by depositing ink droplets formed by the discharge of ink onto a recording medium such as a sheet.
2. Related Background Art
In the facsimile communication, an apparatus allowing for the high speed transmission/reception has various advantages because it can improve the usability and shorten the occupying time on the telephone line, reducing the running cost.
To meet the requirement of higher speed at the reception, not only a receiving control circuit for processing received data but also a recording apparatus must be made faster. Thus, conventionally a recording method was mostly used in which received lines were recorded at one time while conveying the sheet sequentially, using a thermosensible line head capable of recording a received image at high speed.
However, in the recording method using a conventional thermosensible line head, the recording speed is higher, but the recording head is expensive, so that it is difficult to provide an inexpensive facsimile terminal equipment. Furthermore, as the recording sheet is a thermosensible paper, there is a problem that the fading or tarnishing due to a long storage makes it impossible to record onto the recording sheet.
In an apparatus using the so-called serial recording method in which the image reproduction is performed in such a way as to record one line by driving a plurality of recording elements laid on the recording head while reciprocating the recording head, and repeat the above recording plural times while feeding the recording sheet, there have been proposed various recording apparatuses of facsimile as the recording head is cheaper than in the line head recording method. As this method includes several recording methods capable of recording onto an ordinary paper such as so-called wire dot method or thermal transfer method, there is no problem with the preservation of recording papers.
However, most of these methods have the recording speed less than the receiving speed, and generally, when the recording apparatus having a recording speed slower than the receiving speed is used, it is necessary to provide a large amount of receiver buffer such as memory IC within the apparatus, which may increase the cost of the apparatus. Also, there is a method in which image data once received at higher speed is stored in a floppy disk or the like and later recorded at slower speed in the serial recording method, but similarly increasing the cost of the apparatus.
Recently, the recording speed in the serial recording method has been remarkably improved, and there is an attempt to perform the real time recording by reducing the reception buffer to a small amount. Particularly, among the ink jet methods of recording by discharging the ink directly onto the recording sheet, the recording head using the ink jet method of discharging the ink with the pressure of film boiling in the ink caused by electricity-heat converters for generating the thermal energy provided as the energy element for discharging the ink makes it possible to carry out the recording at high speed and high definition, and further to form more recording elements easily within a single head, so that it is optimal for the recording apparatus of the facsimile apparatus which records a received image at high definition and high speed.
On the other hand, in the standards of G3 facsimile, two apparatus constants of horizontal resolution (main scan line density) and vertical resolution (sub-scan line density) are defined.
The main scan line density signifies the number of pixels per mm in a main scan direction (horizontal direction in this case), in which in the G facsimile, there are provided two kinds of densities for a standard resolution of 3.85 pixels per mm (generally called the "standard" or "normal") and a high resolution of 7.7 pixels per mm (generally called the "fine").
Ordinarily, the recording pixel density of a serial recording head is set in accordance with the pixel density in the fine mode in order to record a received image in the fine mode at the same size as a transmitted original without defects of data. Therefore, when the "normal" image is received, the control is made so as to record one pixel with two pixels of the recording head.
Also, usually, at the transmission and reception in the normal mode, it is intended to make the transmission and reception at high speed and thus inexpensively, with almost no considerations of the recording quality of image, but at the transmission and reception in the fine mode, the recording quality of image is more considered than the transmission and reception speeds.
However, as previously described, when the "normal" image is received, the control is made so as to record one pixel with two pixels of the recording head, and the amount of data to be received is less than that in receiving the "fine" image.
Accordingly, the transmission time per unit page of recording data can be essentially less in the normal mode, in which the communication cost can be reduced. However, as previously described, taking into consideration the requirements for the cost reduction and smaller construction of apparatus, it is requisite to constitute the receiver buffer with a smaller capacity, in which when the recording speed is slow, the transmission speed must be also slower on the transmission side, thereby increasing the waiting time unusable for the transmission of data, whereby there was a problem that the occupying time of line would be increased, irrespective of the transmission of the "normal" image data, resulting in a higher running cost.
Thus, in a serial recording method with the ink jet method, or other serial recording methods at higher speed, it is conceived that the recording should be enabled in both directions of reciprocatory movement of the recording head to meet the recording speed corresponding to the reception at high speed, but generally, in a "forward" direction and a "backward" direction of reciprocatory recording, image shift may arise at the juncture between the "forward" and "backward" movements due to a backlash of the driving system for moving the recording head, whereby the image quality might be sometimes degraded.
Also, the recorded image may be sometimes differently formed between the "forward" and "backward" directions due to the shape of the recording head, and the way of depositing the ink may be different between the recording in the "forward" direction and that in the "backward" direction, causing the fluctuation of recording density, whereby there was a problem that the image quality could not be sufficiently obtained in recording the "fine" image.
On the other hand, assuming that the number of lines recordable in one movement of the recording head in the left and right directions is A lines/sec in the line mode, it is A/2 lines/sec in the normal mode because the control is made so as to record one pixel with two pixels of the recording head in the normal mode. By the way, when the transmission rate of image data is 1 lines/sec, a receiver buffer for reserving the image data as large as (1-A/2) lines/sec is necessary in the normal mode if the recording speed is less than the transmission rate. Accordingly, there was a problem that when the recording speed was slow, it was necessary to increase the capacity of required receiver buffer, which may increase the cost of apparatus.